Refactor script generation to make it fully on-demand

- Rename `ShellScript` to `ShellConfiguration` and remove all generated scripts
- Introduce `ShellScriptType` with different types of scripts
- Introduce `GetConfiguration` and `GenerateScript` for `Shell` interface
- Change `ShellScript` to `Shell` of `Executor`
- Remove `GenerateScript` from shells, instead provide a generic method with accepts `ShellScriptType`
- Introduce `executeShellScript` for `Build`, method which is responsible for generating and executing a shell script

@tmaczukin What do you think?


See merge request !189